The present invention relates to an image processing for recording or displaying image on a recording medium based on the image information and, more exactly, relates to an image processing method and an image converting apparatus as well for performing the image processing for recording with ink-jet the medical image information obtained through an inputting device, such as medical photographing device.
These years, there have been invented methods of obtaining medical radiographic information without using a radiographic film made of silver-salt photosensitive material. For example, computed radiography (CR) has become popular; it is a device for reading radiographic image, in which a radiographic image, once stored on an imaging plate comprising mostly of stimulable phosphor, is taken out as an stimulable phosphor light, using an excitation light, and then the light is photoelectrically transferred into an image signal.
Of late, there has been proposed a device called flat panel detector (FPD) that reads out radiographic information using radiation phosphor or radiation photoconductive substance combined with a two-dimensional semiconductor detector such as a TFT switching device.
Besides, other radiographic image inputting devices better than simple radiographic device, for example, a X-ray computer tomographic unit (X-ray CT unit) and a magnetic resonance image generator (MRI generator) have also come into wider use. Most of these medical image inputting devices provide the image information in the form of digital signals.
A method most frequently employed for diagnosing these medical images is to record the image information on a transparent-type recording medium and/or a reflex-type recording medium and observe the image in the form of a hard copy. A recording type most frequently applied to a medical image recorder that records the medical image information on a recording medium is to record image on a transparent-type recording medium, made of silver-salt recording material, by laser exposure. With this recording type, monochrome multi-gradation image can be depicted with excellent gradient and besides, recording the image on a transmission medium and observing it with a transmission light enables to achieve high diagnostic resolution.
Besides, very recently, hopes are laid on a possibility of recording medical image using an ink-jet type recorder.
Though it is desirous for the above-mentioned medical image recorder to depict the image information obtained through a radiographic image inputting device as truly as possible, blurredness unique to each recorder is caused-to the image in practice.
For example, with a type that records image by laser exposure, some blurredness results from a fact that the laser beam has a certain size of diameter. With a so-called thermal recording type in which heat is added per every pixel to record image on a recording medium, blurredness results from a fact that the thermal head has a finite size or from the spread of heat. Even with an ink-jet recording type, blurredness results from various sizes of ink dots generated on a recording medium or from a fact that the coloring material of the ink blots and spreads into or on the recording medium.
Besides, when using a display monitor such as CRT or liquid crystal display, blurredness of image is caused. The blurredness like the above is likely to result in poor diagnostic resolution and wrong diagnosis.
The above-mentioned blurredness of image differs in its level on different medical image recorders and, besides, even on the same medical image recorder, the level of blurredness may vary with the density of image to be recorded. Thus, diagnosis with stable image quality is prevented.
For a laser exposure recording type, for example, reducing the laser beam diameter will be useful to minimize the blurredness of image. This, however, results in a problem that very expensive optical system is needed or that the reduced beam diameter causes recording unevenness and hence the image quality is rather deteriorated. For an ink-jet recording type, reducing the emitted ink particle size will be useful to reduce the ink dot diameter. This, however, also results in a problem that reducing the ink particle size is technically very difficult and that the reduced ink particle size leads to lower recording speed.
Besides, when recording image by the ink-jet recording type, the ink adhesion onto a recording medium may vary with the image density to be recorded. The ease of movement of the color in the recording medium depends upon the ink adhesion onto the recording medium and therefore, the extent of spread of the ink, i.e. the sharpness characteristic varies. As a result, there arises a problem that the sharpness varies with the image density to be recorded and hence stable image quality cannot be attained.
In addition, it may be preferable, to some extent, for a commercial ink-jet printer or similar device that an image after excessive correction of the sharpness may have a different condition from that of the original image (for example, a condition where the sharpness is higher than in the original image). In an application of diagnosing medical image, however, this leads to an inconvenience.